This invention relates generally to the field of mechanical or compression type refrigeration systems of the type frequently employed in commercial and industrial applications for "low" or "medium" temperature applications. In particular, the invention relates to an economical means to convert or "retrofit" refrigeration systems designed for the use of traditional chlorofluorocarbons ("CFC's") , specifically the refrigerant known as "CFC-12" or "R-12," to the use of environmentally more desirable refrigerants having different operating characteristics, in particular, the refrigerant known as "R-22."
Nearly twenty years ago, a theory was espoused that CFC's being released into the environment were reducing the amount of ozone in the atmosphere. Ozone serves as a filter to protect the Earth from harmful ultraviolet rays. In 1987 the National Aeronautical and Space Administration ("NASA") published a report that directly linked CFC's with ozone depletion. Scientists have further stated that during the period 1969 to 1986 the protective ozone layer was reduced 1.7 percent to 3.0 percent in certain latitudes of the Northern Hemisphere. Reduction in the earth's ozone layer has been blamed for the advent of "global warming" with its many side effects, such as an increased risk of skin cancers.
The Clean Air Act Amendments of 1990 contain drastic controls and regulatory requirements for the production and use of CFC's. Among the requirements are phaseouts of the production of certain CFC's and strict regulations regarding the transfer and handling of CFC's. These regulations and controls will significantly affect the costs of servicing, maintaining, and operating refrigeration and air conditioning systems that utilize CFC's. CFC production is being curtailed and is scheduled for total phaseout.
Based on further NASA test results indicating that the accumulation of ozone depleting chemicals in the atmosphere is larger than expected, the governments in both the United States and Japan have recently announced plans to accelerate the "phase out" of CFC production and use.
One of the CFC's targeted by such programs is CFC-12, commonly known to the refrigeration and air conditioning industry as "R-12" refrigerant. Other refrigerants, such as R-22, an "HCFC" refrigerant, are far less damaging to atmospheric ozone than is R-12 due to the fact that they contain substantially less chlorine. Like R-12, R-22 cannot be freely vented to the atmosphere and must be recovered during servicing procedures, but R-22 continues to be "acceptable" under current regulations which permit R-22 to be manufactured without restriction until the year 2020, when it will begin to be phased out by year 2030.
The design of a refrigeration system is generally predicated on the choice of the specific material to be utilized as the refrigerant. R-12 refrigerant has been in use since 1931. Because of excellent stability and a high affinity for oil, R-12 was the predominant choice for use in "low" or "medium" temperature applications. ("Medium" temperature applications are generally those in which the evaporator coil temperature is approximately 5.degree. F. to 20.degree. F., which generally corresponds to a refrigeration "box" temperature of approximately 20.degree. F. to 40.degree. F. "Low" temperature applications are those in which the evaporator coil temperature is 5.degree. F. or lower.) Thus, R-12 was used in the design and operation of refrigeration systems typically employed in restaurants, supermarkets, dairy stores and fast food outlets. The physical and thermodynamic properties of R-12 refrigerant dictated many of the design features of such systems including, for example, the type, size and operating parameters of the compressor.
The phase out of R-12 in favor of other refrigerants, such as R-22, is not a simple matter of removing the refrigerant from the existing refrigeration system and replacing it with the environmentally preferred material, i.e., like an oil change. The physical and thermodynamic properties of R-22 refrigerant are significantly different from those of R-12 such that the refrigeration system operates with different performance parameters (e.g., compressor head temperature and pressure) than those required by R-12. For example, the higher enthalpy characteristics of R-22 means that less refrigerant is required in the refrigeration system, but that the system must be operated at a higher pressure. The low pressure side of a typical compression type refrigeration system utilizes 9 psig. to 29 psig with R-12 and 24 psig. to 54 psig. with R-22; the high pressure side utilizes 136 psig. with R-12 and 226 psig. with R-22. In fact, R-22 refrigerant was designed for "high" temperature applications (i.e., those generally involving the normal range of operation of room air conditioning systems) and not for the "low" and "medium" temperature applications in which efforts are now being made to utilize it as a replacement for R-12.
The invention described herein is intended to apply to refrigeration systems in which the compressor is "rated" for R-12, i.e., it has a published rating for R-12, and possibly also R-502 refrigerant, but not for R-22. Common "wisdom" in the industry is that the R-12 rated compressors in refrigeration systems designed for R-12 must be replaced when converting the system to the use of R-22 refrigerant. (See, for example, "Refrigerants: What's Next," Engineered Systems, March 1991, pp. 50-52; "Using HCFC-22," Heating/Piping/Air Conditioning, November, 1991, pp. 64 to 72). Manufacturers of such equipment have stated that operation of a refrigeration system designed for R-12 with R-22 refrigerant would quickly result in overheating, overloading and destruction of the compressor. Accordingly, all commercially known suggestions to convert existing compression type refrigeration systems designed for the explicit use of R-12 to the use of R-22 or other available substitutes call for the replacement of the compressor. In many systems the conversion from R-12 to R-22 will also require supplementation of existing condenser capacity, primarily through the replacement of this expensive piece of equipment. Thus, users of refrigeration systems with compressors designed and rated for R-12 are confronted with significant costs of replacing equipment that has not completed its useful life.
Conversion of systems designed for R-12 to the use of R-22 is very expensive, particularly for certain industries, such as retail supermarkets and groceries. Because of the differing temperature requirements for the variety of products in a typical supermarket (e.g. produce, dairy products, cheese and meats), each supermarket must have numerous R-12 refrigeration systems, one for each zone with particular temperature needs. The average supermarket has 15 to 25 refrigeration systems with some supermarkets having as many as 40. The cost for a typical supermarket to convert its refrigeration systems from R-12 to environmentally preferred materials requires a minimum of at least one hundred thousand dollars. In addition to these capital costs, the increased capacity of the compressor and the condenser result in significantly increased energy consumption and operating costs on a continuing basis. In contrast, the retrofit system of this invention reduces these capital costs by at least, approximately forty percent (40%) without increasing the energy consumption or operating costs of the resulting retrofit system.
Many supermarket chains and refrigeration equipment suppliers have been concerned about the cost of the CFC conversions and have been searching for solutions to the problem. Nevertheless, prior to my invention no one has found an economical way to utilize the environmentally preferred refrigerants in existing commercial and industrial refrigeration systems designed for the use of R-12. Attempts have been made to utilize other refrigerants to replace R-12 without requiring expensive equipment replacement. These efforts have been unsuccessful. And despite significant economic incentives, to date refrigerant suppliers have been unable to develop a direct, i.e., "drop in," replacement refrigerant to substitute for R-12 which: (1) poses significantly reduced environmental risks, and (2) has physical and thermodynamic properties similar enough to R-12 that expensive equipment replacement is not required in the conversion of existing R-12 based systems.